I came across this quote from A.W. Pink in his book The Sovereignty of God. I found these words convicting, humbling, and encouraging:

"We readily acknowledge that it is very humbling to the proud heart of the creature to behold all mankind in the hand of God as the clay is in the potter's hand, yet this is precisely how the Scriptures of Truth represent the case. In this day of human boasting, intellectual pride, and deification of man, it needs to be insisted upon that the potter forms his vessels for himself. Let man strive with his Maker as he will, the fact remains that he is nothing more than clay in the Heavenly Potter's hands, and while we know that God will deal justly with His creatures, that the Judge of all the earth will do right, nevertheless, He shapes His vessels for His own purpose and according to His own pleasure. God claims the indisputable right to do as He wills with His own." 

-A.W. Pink, The Sovereignty of God, p.52